The present invention relates to an image forming apparatus.
In a conventional image forming apparatus, a static latent image is formed on a photosensitive drum, and the static latent image is developed with toner, thereby forming a toner image. A transfer device transfers the toner image on the photosensitive drum to a medium, and a fixing device fixes the toner image to the medium through heat and pressure.
In the conventional image forming apparatus, when a medium transport device transports the medium, the medium may be curved between, for example, the transfer device and the fixing device due to a difference in medium transport speeds. When the medium is curved excessively, the image on the sheet may contact with a component in the conventional image forming apparatus, or the medium may be wrinkled or jammed. When the medium is extended excessively, the image may be shifted, or a transport motor may be detached.
To this end, in the conventional image forming apparatus, when the medium transport device transports the medium, a slack of the medium is detected for adjusting the medium transport speed of the medium transport device or the fixing device, thereby preventing the problems described above. An example of detecting the slack of the medium includes a combination of a lever arm and a photo-coupler sensor.
Patent Reference has disclosed technology for adjusting the medium transport speed. According to Patent Reference, an image forming apparatus includes a transport unit for transporting a medium supplied thereto; an image supporting member disposed on a downstream side of the transport unit in a transport direction of the medium; a transfer unit disposed to face the image supporting member for transferring a latent image on the image supporting member to the medium; and a slack removal portion disposed between the transport unit and the transfer unit for forming a slack in the medium.
Patent Reference: Japan Patent Publication No. 09-325544
In the conventional image forming apparatus, a medium slack detection unit detects the slack of the medium through an on/off operation, thereby adjusting the medium transport speed on an upstream side or a downstream side of the slack detection unit. Accordingly, when just one medium is transported with a variance in the medium transport speed, it is difficult to properly adjust the medium transport speed according to a transport state of the medium.
As a result, the medium transport speed may vary according to a type of medium, a variance in the units, a change in a temperature of the apparatus, and the likes. That is, it is difficult to detect an excessive slack, thereby causing a winkle or a jam. When the slack is not so excessive, the medium may be accelerated excessively. Accordingly, the image may be shifted, or a transport motor may be detached, thereby making it difficult to stably obtain the transport speed.
In view of the problems described above, an object of the present invention is to provide an image forming apparatus capable of solving the problems of the conventional image forming apparatus.
Further objects of the invention will be apparent from the following description of the invention.